(1) Field of the Invention
The present invention relates to a zoom lens, more particularly to a zoom lens assembly for a zoom camera which heightens mechanical strength and improves shading efficiency between a front move barrel and a shutter.
(2) Description of the Prior Art
A zoom lens has an advantage of being capable of varying a focal length successively by adjusting an external ring.
A zoom lens has been used as an exchange lens of a single reflex camera. In recent days, a new kind of camera called a zoom camera has been further developed by mounting a zoom lens on a snapshot type camera.
Generally, a conventional zoom lens assembly for a zoom camera includes a guide barrel which is to be fixed to a camera body, a front move barrel which is telescopically mounted within the guide barrel and a cam barrel which is rotatably mounted about the guide barrel. In addition, the guide barrel is provided with a plurality of linear slots, the rotatable cam barrel is provided with a plurality of spiral slots, and one or more rollers is secured to the front move barrel to project through the linear slots of the guide barrel into the spiral slots of the cam barrel so that upon rotation of the cam barrel, the front move barrel is caused to move into and out of the guide barrel.
In addition, a lens group and a shutter are usually mounted at the front of the front move barrel.
A shading tape has also been coated on the outer circumference of rotatable cam barrel so as to prevent the permeation of light through the overlying slots of the cam barrel and guide barrel.
In order to be able to rotate the cam barrel, a ring gear has been provided at one end of the cam barrel so as to be driven by a suitable motor. Thus, upon activation of the motor, the front move barrel can be moved forward or backward so that the focal length of the lens group can be varied.
Typically, the cam barrel has been made of aluminum since such a material can be readily shaped and is of light weight. However, the mechanical strength of aluminum is weak so that the cam barrel must be made of a relatively large thickness. This, in turn, makes the size of the cam barrel relatively large. Thus, the bulk of the camera is increased and carrying of the zoom lens assembly becomes inconvenient.
Further, since the shutter is assembled in the direction of the axis of the front move barrel, care should be taken to avoid having an aperture between the shutter and the front move barrel through which light may pass.